Articles incorporating a polymer foam core are characterized by the density of the foamed polymer being lower than the density of the pre-foamed polymeric matrix. The lowered density for the foam may be achieved in several known ways such as by the use of a blowing agent to generate gas-filled voids within the matrix or by interspersing microspheres within the matrix, the microspheres typically being made of glass or of certain polymeric materials.
Articles that include polymer foams are described, for example, in U.S. Pat. No. 6,103,152 issued on Aug. 15, 2000 to Gehlsen et al. The Gehlsen '152 patent describes articles that include a polymer foam featuring a polymer matrix and one or more expandable polymer microspheres. The foam microstructure is characterized by a plurality of enlarged polymeric microspheres distributed throughout the polymer matrix. At least one of the microspheres is still expandable, i.e., upon application of heat it will expand further without breaking. The foam may be formulated with an adhesive surface and is characterized by a surface that is substantially smooth.
Any of a variety of articles can include a polymer foam core such as, for example, vibration damping articles, medical dressings, retroreflective sheeting, tapes, anti-fatigue matting, abrasive articles, gaskets, sealants, and the like. In the aerospace, electronic, and automotive industries, for example, foam core tapes may be used in the assembly and/or attachment of parts and panels. However, the foam core tape products currently available provide bonds between the attached surfaces that are more or less permanent, making it very difficult to later separate the parts and, consequently, difficult to recycle those parts. Certain regional areas, for example, Europe, require product life management, and material contamination is an issue in this regard.
Adhesive materials, including pressure sensitive adhesives, are commercially available for use in any of a variety of applications. Certain pressure sensitive adhesives comprise a fibrous reinforcing material like that described in U.S. patent application Ser. No. 09/764,478. The patent application describes the fibrous reinforcement of pressure sensitive adhesives to provide “stretch removable” characteristics. The fiber reinforced adhesive composition comprises a pressure sensitive adhesive matrix with a fibrous reinforcing material therewithin. The fiber reinforced adhesive composition is described as providing improved cohesive strength over the pressure sensitive adhesive alone, while the tack of the pressure sensitive adhesive remains substantially unreduced by the presence of the fibers.
In order to address a long felt need in the manufacture and use of adhesives, and particularly in foam core tapes, it is desirable to provide tape having strong bonding characteristics when applied to a surface. It is also desirable to provide an adhesive composition for use in a foam tape wherein the adhesive is formulated to facilitate the removal of the foam tape from the aforementioned substrate by a stretch release mechanism. The technical requirements of a foamed stretch release tape have been thought to include (1) foam split strength at least about 10 lbs/in (1.76 kN/m); (2) 90 degree peel adhesion greater than about 10 lbs/in (1.76 kN/m), (3) high tensile strength that is generally higher than the force required to remove the tape from a surface so that the tape is not broken upon stretch release; (4) mechanical properties including a low yield stress, good elongation (e.g., >200%) and (5) either have significant strain hardening behavior or high elastic recovery.
Conventional foam tapes have generally been designed to provide more permanent (e.g., not releasable) attachment systems in any of a variety of industrial applications. Hence, such attachment systems have been provided as high strength attachment systems generally incapable of being easily released from a substrate. Moreover, the high strength bonds provided by conventional foam tapes have been incompatible with the notion of formulating a foam tape that is stretch releasable along with having desirable adhesive qualities.
It would be desirable to provide stretch releasable foam core substrates, articles including such substrates (e.g., tapes), and methods for the manufacture of the articles. It is also desirable to provide these substrates using a soft pressure sensitive adhesive foam matrix that allows for energy dissipation and a high tensile strength to provide strong adhesion to any of a variety of surfaces.